[.NET Web API2] 要如何在ModelBinding falied送出我想要的错误讯息格式

.NET VERSION : .ner framework 4.6.1 WEB API 2

如果我需要在ModelState.isValid == false时, 送给前端特殊格式应该怎么做？

这里假设我需要传送给前端的错误讯息是"|object.property: xxx为必填|object.property:XXX格式不正确"的时候
应该要怎么写我的Filter呢？

public class ValidateModelFilterAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(HttpActionContext actionContext)
    {
        if (actionContext.ModelState.IsValid == false)
        {
            var sbError = new StringBuilder(128);
            foreach (var model in actionContext.ModelState)
            {
                var message = model.Value.Errors.FirstOrDefault().ErrorMessage;
                message = (string.IsNullOrEmpty(message)) ? model.Value.Errors.FirstOrDefault().Exception.Message : message;
                sbError.Append($"|{model.Key}:{message}");
            }

            actionContext.Response = actionContext.Request.CreateErrorResponse(
                HttpStatusCode.BadRequest, sbError.ToString());
        }
    }
}

[ValidateModelFilter]
public IHttpActionResult Post(LoginModel login)
{
   ...
}